The older German patent application P 199 49 507.4 by the applicant describes several gear patterns for an automatic multi-step reduction gear with various combinations of coupled planetary gear sets. Through the suitable connection of a non-shiftable front-mounted gear group combination to a shiftable rear-mounted gear group combination at least seven forward gears can be switched, respectively, without a multiple connection. The number of shiftable forward gears is hereby greater than the number of switch elements by a factor of at least two.
DE-P 199 49 507.4 suggests the development of the shiftable rear-mounted gear group combination as a two-planet carrier/four-shaft transmission with two shiftable rear-mounted planetary gear sets. A two-planet carrier/four-shaft transmission should be interpreted here as an arrangement of two individual mechanically coupled single carrier planetary gear sets where the coupled unit contains four so-called “free shafts” due to the double component connection feature, wherein a “shaft” can be a sun wheel, a ring gear or a planet carrier of a planetary gear set.
It is now the object of the present invention, proceeding from the known state-of-the-art, to develop further a multi-step reduction gear with at least seven forward gears that can be shifted without a multiple connection with comparatively little construction effort, unmodified favorable gear steps and large spread.